1. Field of the Invention
The present invention relates to a developing agent bearing member used in a developing unit of an image forming apparatus of an electrophotographic or electrostatic recording scheme, and a method of manufacturing the developing agent bearing member.
2. Related Background Art
A developing unit for developing and visualizing an electrostatic latent image carried on an electrostatic latent image bearing member is known as a developing unit used for an image forming apparatus such as an electrophotographic copying machine. In a developing unit of this type, a developing agent bearing member (developing sleeve) made of a metal is generally used to carry a developing agent accommodated in a developing vessel onto the developing sleeve and convey it to a developing region opposing the electrostatic latent image bearing member. The electrostatic latent image formed on the electrostatic latent image bearing member is developed with the developing agent to visualize the electrostatic latent image as a developing agent image. As a developing agent, a one-component developing agent containing a magnetic toner, a one-component developing agent containing a nonmagnetic toner, a two-component developing agent containing a nonmagnetic toner and a magnetic carrier are available. The material of the developing sleeve is selected depending on the type of developing agent. When a magnetic developing agent is used, a nonmagnetic metal is used as the material of the developing sleeve. In this case, a magnetic field generating means such as a magnet is arranged inside the developing sleeve. To perform good development, a developing bias is applied to the developing sleeve during development. As the bias, an AC voltage, a DC voltage, or a voltage obtained by superposing AC and DC voltages is used. As a metal for the developing sleeve applied with this voltage, a conductor is often used.
In conveying the developing agent on the developing sleeve to the developing region using the developing unit having the above arrangement, conveyance of the developing agent can be improved by roughening the surface of the developing sleeve, and the surface of the developing sleeve can be coated with a developing agent layer.
As a method of roughening the surface of the developing sleeve, a sandpaper method for abrading the surface of the developing sleeve with sandpaper, a bead-blast method using spherical particles, a sandblast method using particles having indefinite shapes, a combination thereof, a chemical etching method using chemical treatment, or the like is proposed and used in practice.
The entire surface of the developing sleeve may be coated by spraying, dipping, or the like with a resin mixed with a conductive powder.
As disclosed in, e.g., Japanese Laid-Open Patent Application No. 4-212183, a structure in which an insulating region surface is formed on the surface of a developing sleeve, and a conductive region surface is formed thereon is proposed.
The conventional developing sleeves pose the following problems.
The size of the uneven portion on the surface and its distribution state become nonuniform in a metal developing sleeve whose surface is roughened. For this reason, the convey amount of the toner becomes nonuniform, and image defects such as density irregularity and a decrease in density occur, or the resistance value on the surface of the developing sleeve cannot be controlled. It is not only difficult to control the image characteristics such as density irregularity and a decrease in density, but also difficult to optimize the resistance of the surface of the developing sleeve depending on different types of toners, thereby often degrading ghosts.
Roughness control performed by only coating conditions for a developing sleeve whose entire surface is coated with a resin is limited. The surface of the developing sleeve serving as a base must be roughened. This results in an increase in the number of steps and complicated determination of operational conditions. Since the size of the uneven portion of the surface and its distribution state are nonuniform like the developing sleeve whose surface is roughened. Therefore, the convey amount of toner and the charge amount become nonuniform, thereby causing image defects such as density irregularity, a decrease in density, and a ghost.
When the surface of a developing sleeve is simply constituted by a large number of insulating and conductive regions for forming an electric field distribution, the electric field distributions between the individual insulating regions are apparently different from each other depending on the shapes of the insulating regions on the sleeve surface even if the sleeve surface is smooth. It is apparent that when an uneven portion is formed in either or both of the insulating and conductive regions of the sleeve surface, the electric field distributions become different from each other. In particular, when the uneven portion is formed in the conductive region, the electric field concentrates on the projecting portion of the uneven portion, thereby apparently localizing the electric field distribution. Therefore, the charge amounts of the respective toner particles are different from each other to result in large density variations, which may also cause the ghost.